Effects of nonlinearity and substrate's deformability on modulation instability in NKG equation

This article investigates combined effects of nonlinearities and substrate's deformability on modulational instability. For that, we consider a lattice model based on the nonlinear Klein-Gordon equation with an on-site potential of deformable shape. Such a consideration enables to broaden the description of energy-localization mechanisms in various physical systems. We consider the strong-coupling limit and employ semi-discrete approximation to show that nonlinear wave modulations can be described by an extended nonlinear Schrodinger equation containing a fourth-order dispersion component. The stability of modulation of carrier waves is scrutinized and the following findings are obtained analytically. The various domains of gains and instabilities are provided based upon various combinations of the parameters of the system. The instability gains strongly depend on nonlinear terms and on the kind of shape of the substrate. According to the system's parameters, our model can lead to different sets of known equations such as those in a negative index material embedded into a Kerr medium, glass fibers, resonant optical fiber and others. Consequently, some of the results obtained here are in agreement with those obtained in previous works. The suitable combination of nonlinear terms with the deformability of the substrate can be utilized to specifically control the amplitude of waves and consequently to stabilize their propagations. The results of analytical investigations are validated and complemented by numerical simulations. (C) 2017 Elsevier B.V. All rights reserved.